1. Field of the Invention
The present invention relates to papermakers fabrics, more particularly to a press fabric resistant to nip rejection and a method for making same.
2. Description of Related Art
Wet press felts are used in the press section of papermaking machines to transport and dewater an aqueous paper web which is being made into a desired paper product. The dewatering process conventionally entails transporting the aqueous web through a series of press nips. The aqueous paper web is carried on a press felt through at least one nip defined between two metal rolls which squeezes water from the paper web into the underlying press felt.
When in use, press felts are under tension to maintain uniformity in the fabric. However, this tension combined with the high pressures in traveling through the nip may not be sufficient to straighten the press felt yarns just before the press felt enters the press nip. If the press nip load is high and the felt yarns are not straight, they may exhibit a type of scissoring effect which results in a collection or bunching up of yarns at the entrance to the press nip known as nip rejection. Nip rejection is undesirable since it can damage the press felt fabric and cause undesirable marking or irregularities in the paper product itself.
Nip rejection can be combated by increasing the tension in the fabric through the nip. However, many papermaking machines cannot physically exert the amount of tension on the fabric needed to consistently eliminate nip rejection problems. In addition, after running for a day or two, the effects of the added tension disappear since the caliper of the fabric is decreased due to maximum allowable stretching of the fabric. In addition, excessive tension of the press fabric increases the potential for "roping" or "folding over" of the fabric which can result in complete wreckage of the fabric, damage to the paper product and possible damage to the papermaking machine.
It would be desirable to provide a press felt which is resistant to nip rejection.